Fuel Filter Remove=Trapped Air?

[imp]

'04 Expl. 4.0L SOHC, 110K, runs good, preparing for 4 month long trip, so....
best replace fuel filter. Located it, removed it, fair amount of gasoline dribbled out of both fuel lines. About 1/2 teaspoon of really black **** came out of filter!

Then got to thinking: Returnless fuel system, only pressure line feeds to fuel rails, just enough fuel to meet engine demand. So, a big gob of air gets introduced within the lines and new filter, pump pushes that air to the fuel rails, injectors get AIR, not gas, NO?

So, conferred with Ford Shop Manual, "Replace Fuel Filter", no mention of air at all! I put the new filter in, turned key to "on" 2 times, just to be sure, cranked engine normally, started and ran immediately, smooth, no problems (or LEAKS, either!).

What the hell becomes of that trapped air?? Anybody know? It's buggin' me! imp

 

[BigRondo]

'04 Expl. 4.0L SOHC, 110K, runs good, preparing for 4 month long trip, so....
best replace fuel filter. Located it, removed it, fair amount of gasoline dribbled out of both fuel lines. About 1/2 teaspoon of really black **** came out of filter!

Then got to thinking: Returnless fuel system, only pressure line feeds to fuel rails, just enough fuel to meet engine demand. So, a big gob of air gets introduced within the lines and new filter, pump pushes that air to the fuel rails, injectors get AIR, not gas, NO?

So, conferred with Ford Shop Manual, "Replace Fuel Filter", no mention of air at all! I put the new filter in, turned key to "on" 2 times, just to be sure, cranked engine normally, started and ran immediately, smooth, no problems (or LEAKS, either!).

What the hell becomes of that trapped air?? Anybody know? It's buggin' me! imp

Let it go man!! Get some sleep and attack it in the morning. I'm hitting the rack, but I am subscribed so I'll check it out in the AM.

 

[BradR]

Didn't you read the fuel filter howto?! You'll have to replace your injectors in a month, and they're EXPENSIVE!











JUST KIDDING!
ahahha.
Happy Halloween!

 

[imp]

JUST KIDDING!
ahahha.
Happy Halloween!

Sure glad you added this!! imp

 

[jakedrew]

haha.


Never thought about the air. BUT My guess is that it gets pushed through the injectors.

 

[imp]

haha.


Never thought about the air. BUT My guess is that it gets pushed through the injectors.

That's what I've been thinking, too, but.... Each time an injector opens to feed fuel, it squirts a small fraction of a DROP of gasoline. So, it should take a long time to bleed out so much air.......meanwhile, the engine would likely not run at all. imp

 

[1AJeremyD]

as long as the key is cycled a few times you will be all set. Diesels are the only ones that need to bleed before running. The injectors just push the air out since they are not squirting at such a high pressure as a diesels are yet I don't know about the new direct injected engines and how those work with a fuel filter change because those are in the thousands of PSI

 

[SuRrEaLNJ]

gas is idiot proof, cycle the key and your fine, any air that was in the system will be pushed through by the new fuel

diesels need to be primed or they will air lock, but thats something entirely different and nothing to worry yourself about

 

[imp]

as long as the key is cycled a few times you will be all set. Diesels are the only ones that need to bleed before running. The injectors just push the air out since they are not squirting at such a high pressure as a diesels are yet I don't know about the new direct injected engines and how those work with a fuel filter change because those are in the thousands of PSI

This may be the key! The "slug" of air which gets in via the filter and lines, is at 14 psi, but when the fuel pump squeezes it with gasoline at 40 psi or more, the air is squashed down to maybe 1/3 it's size......but still, a lot of air to bleed out through those little injector nozzles. Just can't explain how the engine started and ran perfectly normally........ imp

EDIT: For anyone interested, typical injector "lift" is about 0.006", that's 3 human hair thicknesses, the injector valve being open for only milliseconds at a time. I have Ford published numbers regarding amount of gas squirted by each injector cycle, if anyone is interested, please ask!

 

[jakedrew]

maybe think of the concept as a "fart" ? Doesnt matter how much "air" is in there, it will get pushed out as soon as the "opening" opens.

 

[waskly]

think about of all the air that flows in when you pump fuel into the tank! o.o

 

[waskly]

I have Ford published numbers regarding amount of gas squirted by each injector cycle, if anyone is interested, please ask!

?? never heard of this.

i'm interested.

 

[imp]

think about of all the air that flows in when you pump fuel into the tank! o.o

Please explain more, I'm confused! All of the air that flows in ....to where?

We pump fuel into a tank full of air, the air is replaced by the liquid, and leaves the tank around the fill nozzle, NO? imp

 

[waskly]

Please explain more, I'm confused! All of the air that flows in ....to where?

We pump fuel into a tank full of air, the air is replaced by the liquid, and leaves the tank around the fill nozzle, NO? imp

well a tank is not a sump system.

it has a pump on the bottom of the tank, and it goes upwards.

now air is lighter then gas, so as gas is pumped in the air should go into the fuel system also.

only from the pump fuel vapors are released at the filler neck

the air in the tank is purged through a valve away from the filler neck. into a charcoal canister to remove the smell....

 

[imp]

?? never heard of this.

i'm interested.

Now I'm flattered! Usually it is I who am interested in your comments, not the other way around!

Anyhoo, I dragged out the book of Ford Fuel Injection and scanned a couple of pertinent paragraphs. Unfortunately, my damn dial-up sevice took 7 MINUTES to download that one page to where I could do something with it! Far too time-consuming, so I hope if I excerpt some by just writing a few facts, it will be of value for you.....

Ford injectors: Valve seats on conical body, clearance between pintle and housing is 0.002" (0.05mm). The pressurized fuel must pass through this tiny clearance, and sprays on specially-shaped pintle tip to atomize fuel.

Injector "size" is stated in volume or weight of fuel capable of delivering if injector were "open" (energized) continually. 5.0L HO Mustang engine used 19 LB/hour injectors, meaning each would deliver 19 LBS. of fuel in an hour, if kept open (at rated pressure 39psi). '93 Cobra 5.0L used 24 LB/hr., therefore requiring different Mass Air and PCM calibrations.

"Pulse Time" is how long the injector is "open", or delivering fuel, for each firing cycle of it's cylinder. Given that engines must be able top run fast, say 6,000 rpm, the time available for each injector Pulse Time is VERY SHORT. Ford operates within the envelope of 1 ms to 15 ms (ms=millisecond, 1/1000 sec.). So, if Pulse Time is 1ms with 19lb/hr injectors, each injector delivers 0.0000053 lb. of fuel each time it opens; that's 5.3 millionths of a lb (5.3/1,000,000). At max. Pulse Time, 15ms "open", 0.000079 lb (79/1,000,000 lb). Stated differently, at max Pulse Time, that injector must open & close about 12,600 times to deliver a pound of fuel. And, that scenerio would be happening with the engine producing it's maximum HP.

Ford injectors typically use pintle "lift" of 0.15mm, or 0.006". The amount the injector opens, or "lift" is fixed; it always opens 0.006" no more, no less. Amount of fuel delivered is therefore dependent on 2 things primarily, if we ignore things like fuel viscosity change, those 2 being fuel pressure, and Pulse Time. Pressure is held constant, so all the computer must do is tell the injector how long it should be open, to meet the demands being placed on the engine.

The discussion can get much deeper; for example, "Divided-Spray" injectors deliver 2 shots simultaneously, angled away from each other, and aimed into the intake ports of DOHC engines.

Out of time for tonight, sorry! imp

 

[waskly]

i was interested in this since i know some time in 02 they changed injector pulse on same lb injectors. from 10-20ms to 100's of ms.

 

[1AJeremyD]

crazy to think that those are things are moving at that rate of speed! Thanks imp for the thread!

 

[waskly]

diesels need to be primed or they will air lock, but thats something entirely different and nothing to worry yourself about

lol? sorry but no, that whole low pressure manual fuel pump system has been gone a long time. they are the same as gas.

both are idiot proof. diesel i think even more.

 

[imp]

crazy to think that those are things are moving at that rate of speed! Thanks imp for the thread!

The reason injectors can operate fast enough to sustain 6000 rpm or more, is the very small amount that their inner mechanisms move (0.006", approx.). Their parts inside are very small, since each squirt of fuel is just a tiny bit, and smal;l moving parts have low inertia, which means they don't "pound themselves silly"!

For an average vehicle, say an Explorer (!), with let's say axle ratios of 3.53, and usual tire size, maybe 29" rolling diameter, and overdrive gear, each injector in the engine "fires" about 1000 times, if at 60 mph, that's 1000 times each minute! Or, 17 times a second.

So, obviously, the computer's ability to "work fast" was most important in EFI working acceptably. Please be aware, the computer's "program" consists of thousands of steps, which it must "scan" repeatedly, over and over, faster than the time interval between successively firing cylinders, or the scheme could not work at all! As it scans, it looks at the various inputs from sensors, and makes instant decisions regarding injector "open" time, when to make the spark plugs fire (spark advance is constantly being controlled), what to do about the "closed-loop" control being exerted on the operation by the Oxygen Sensors, and all the while maintaining the level of engine power output being asked for by the driver. Interestingly, in recent years, the driver has lost "absolute control" over power demand, as "drive by wire" now allows the computer to reduce engine power if certain things occur which might prove damaging to the engine, such as high oil or water temperature. My concern for losing this control as a driver is: what if a burst of flat-out power is needed to safely pass on a 2-lane road, and just then, the computer decides to limit power output? Food for thought! imp

 

[imp]

i was interested in this since i know some time in 02 they changed injector pulse on same lb injectors......

from 10-20ms to 100's of ms. And I am interested in THIS...

Consider that at 6000 eng. rpm, each piston must make it's journey up and down within it's cylinder 100 times every second! Given 4-cycle operation, each injector must "fire" 50 times per second: that's ONCE EVERY 20 milliseconds (0.02 sec.). Picture in your mind exactly WHEN the injector must fire: sometime either just BEFORE the intake valve opens, or immediately AFTER it starts to open, (depending on the particular engine) and the "squirt" of fuel must CEASE well before the piston reaches bottom of stroke, so the "time window" during which the injector can be open is much less than even 20 ms, and probably less than 10 ms.

These rate of operation facts are indisputable, if the crank is to turn at 6000 rpm. Long injector pulse times COULD be used at low engine speeds, but to achieve that, and still allow high-speed operation would require much reduced fuel pressure at those low speeds. (The discharge cross-sectional area of the injector's orifice is fixed by manufacture). I don't THINK they are varying fuel pressure to achieve this, but then my "THINKS" have often been wrong before!! imp